Editor's note: This is Part 7 of a series reviewing Michigan’s 2018 position groups and looking ahead to 2019.

Some replacements are difficult and some are simple.

Devin Bush Jr. fits the former category.

"We have our defensive huddle in between series that we sit and this guy always sat to my right, he was always there," Michigan defensive coordinator Don Brown said of Bush at the team awards banquet in December, his voice cracking. "He's the MIKE linebacker. He's one tough guy. Really proud of him. Devin Bush Jr."

Other players, perhaps, garnered more attention. But the central, and most important, piece of Brown's 2017 and 2018 defenses (groups that finished No. 3 and No. 2 nationally, respectively) was Bush.

Michigan's Devin Bush Jr.(Photo: Detroit Free Press-USA TODAY Sports)

A two-time All-American and one of the most unique inside linebackers Michigan has ever had, Bush was not only one of Michigan's smartest players, but he often served as the ultimate eraser because his athletic ability and football IQ allowed him to fix mistakes on the fly.

He played sideline-to-sideline, he was active in the blitz game, he could cover and he rarely missed a tackle.

Michigan has to replace a lot defensively this season. But replacing Bush will be Brown's biggest challenge.

2018 recap

Bush played at an All-American level once again all season long, finishing as a consensus pick before departing early for the NFL draft as one of the more unique defensive prospects in the country.

Through the first 11 games, Michigan strung together some dominant performances at every level defensively, and linebacker was no exception.

Behind Bush, the Wolverines sprinkled in more time for Ross, who appears to be the top candidate to replace Bush, as he rotated with Gil as a weakside linebacker. Michigan went with Furbush, at times, at strong-side in three linebacker sets.

Hudson had an interesting year. He was ejected for targeting in back-to-back weeks and never seemed to find the type of explosive flow that highlighted the back half of a breakout 2017 season. He had 18 tackles for loss in 2017 compared to three in 2018. Michigan finished 2018 with 26 fewer TFL than it did a season ago.

Being elite on a consistent basis isn't easy. Hudson found that out in 2018 and will have one more shot to find that groove again.

Like most areas of Michigan's defense in 2018, there's pre-Ohio State and post-Ohio State.

Michigan can tweak scheme to help these guys in certain situations, but finding a replacement for Bush remains the top priority.

2019 outlook

It'll be an interesting spring and fall camp at linebacker for Michigan. Not necessarily for starting spots, but for depth overall.

Hudson is a two-year starter and could be looked at as a leader on this team. Ross looks like a player on the inside. Gil has plenty of experience. But those jobs might not be set in cement. McGrone was a 5-star prospect out of Indianapolis last year, and impressed the staff with the way he wrapped up bowl practice. He's probably versatile enough to play either inside spot.

There are mysteries everywhere else. Anthony is entering his third year, Haskins and VanSumeren were offensive recruits who played some linebacker last season, and Uche seems like a better fit at defensive end.

Bottom line

Michigan can replace Bush's production from a statistical standpoint, but the Wolverines aren't likely going to be able to replace the full package in one season. There's not another player on this roster with experience that's an athletic and instinctive equal.

There are, however, nice prospects with potential. Ross has the goods to be a solid player. We'll see on McGrone. And for Hudson, it's one last chance to show NFL teams what he can do.

The entire front seven is going through sizable change and will enter spring ball with depth issues.

This isn't the first time Brown has dealt with that. He lost nearly his entire starting defense after the 2016 season, and still wound up with a top-three unit.